The invention relates to fluid injection devices, and more particularly, to fluid injection devices integrating piezoelectric sensors and methods of analyzing fluid in fluid injection devices.
Fluid injection devices have been applied in information technology industries for decades. As micro-system engineering technologies have progressed, fluid injection devices have typically been employed in inkjet printers, fuel injection systems, cell sorting systems, drug delivery systems, print lithography systems and micro-jet propulsion systems. Among inkjet printers presently known and used, fluid injection devices can be divided into two categories continuous mode and drop-on-demand mode, depending on the fluid injection device.
According to the driving mechanism, conventional fluid injection devices can further be divided into thermal bubble driven and piezoelectric diaphragm driven fluid injection devices. Of the two, injection by thermally driven bubbles has been most successful due to its reliability, simplicity and relatively low cost. No matter which kind of injection device is selected, in situ analysis of ink in a fluid injection device is an important issue in replacing an ink cartridge. If the amount of ink in the fluid injection device is inadequate, not only does print quality deteriorate, but, the fluid injection device itself, such as a heater, can also be damaged due to a dry firing effect.
U.S. Pat. No. 5,699,090, the entirety of which is hereby incorporated by reference, discloses a thermal bubble driven ink jet printhead. By measuring the average in resistance dependent on temperature change, the amount of ink in an inkjet printhead can be estimated.
FIG. 1 is a block diagram of methods for optimizing printing parameters for a conventional inkjet printhead. After a controller 111 receives and processes printing data, operating signals are transmitted to a printhead driver circuit 113. A voltage control power supply 115 provides a control voltage VS to the printhead driver circuit 113. The magnitude of the control voltage VS is controlled by the voltage control power supply 115. The printhead driver circuit 113 controlled by the controller 111 provides a driving voltage pulse VP to heaters 117 of the thermally driven inkjet printhead 119, thereby triggering inkjet injection. Subsequently, a temperature sensing resistor 123 on the inkjet printhead 119 can be provided as reference for each heater 117 of the thermally driven inkjet printhead 119. An analog signal is output to analog/digital (A/D) converter 125 according to the comparison between temperature sensing resistor 123 and each heater 117, thereby optimizing printing parameters for the thermal bubble driven inkjet printhead.
FIG. 2 sets forth a representative graph of normalized printhead temperature plotted against time. The graph of FIG. 2 indicates different phases of operation of the heater resistors of a printhead. The control circuit for the inkjet printhead can depend on the graph of FIG. 2 to optimize printing parameters. The graph of FIG. 2, however, can be affected by materials of the temperature sensing resistor, circuit layout, and positions of the temperature sensing resistor. Current passing through the temperature sensing resistor may cause increased temperature, affecting accuracy of the graph of FIG. 2. Measurement of ink content in the inkjet printhead using the temperature sensing resistor 123 is intrinsically limited and not applicable to non-thermally driven injection devices.